This invention relates to fasteners and, more particularly, to an adhesively secured fastener.
The prior art has encountered very serious difficulties when it is desired to fasten friable structures together. The principle behind fasteners such as nails and screws is development of intense but directionally controlled forces between them and the components they are designed to fasten together. This translates into reliance for the fastening function upon the resultant frictional forces between the fastener and the component. The friable material inelastically deforms, as the frictional forces of the fastener act upon it, reducing frictional forces between the fastener and friable material. As a result the fastener is no longer able to secure the structure.
There have been suggestions in the prior art for introducing adhesives to the fastener assembly to increase the fastening strength. The fastening strength is increased because of the chemically induced cohesive forces associated with adhesives.
In U.S. Pat. No. 4,514,125, Stol discloses a fastener including introduction of a capsule of adhesive into a porous basket hung in a bore for activation by fastener installation. In that patent, an adhesive capsule support basket is placed at a desired level into a bore which is about to receive a fastener such as a bolt or screw. A capsule containing adhesive is inserted into the bore and becomes supported by the basket. As the fastener is installed, it contacts and bursts the capsule, spreading the adhesive at the fastening region. A disadvantage of this method consists in that the amount of adhesive which is spread throughout the bore hole is limited to the amount of adhesive within the capsule. Thus, if the attachment of porous structures is desired, the adhesive may not be able to fill the pits and voids required to ensure a satisfactory bond.
U.S. Pat. No. 4,370,372 to Higgins et al discloses a method of joining honeycomb panels using a fastener element. In the arrangement disclosed by this patentee, a hollow tubular fastener with side apertures is inserted through aligned bores in the honeycomb panels. A fluent adhesive is forced into the fastener so that some of the adhesive extrudes through the side apertures to occupy adjacent space in the cellular structures of both panels, thus permanently bonding the honeycomb panels. A disadvantage of this method consists in that the fastener is limited to the bonding of highly porous material. If the fastener is used for bonding nonporous material such as metal or semiporous material such as wood or concrete, the apertures will be blocked by the relatively smooth sidewalls of the bored material. Thus, adhesive forced into the fastener will not extrude through the side apertures and no chemo-mechanical bond will form.